Conventionally, a water pump for use in an engine cooling system includes a power driven impeller shaft having one end portion connected with a power source such as an output member of an internal combustion engine with the other end being provided with an impeller for drawing water from a source of water such as a water tank and forcing the water to an outlet of the pump. The shaft is mounted on a pump housing for rotation about the axis of the shaft by means of a bearing located at the end portion of the shaft adjacent to the driving power source. The impeller is rotated in the pump chamber together with the impeller shaft to force the water in the pump chamber to the pump outlet.
In order to prevent water in the pump chamber from leaking under the pump pressure prevailing in the pump chamber through the impeller shaft to the bearing, the shaft is provided with a mechanical seal that is mounted on the shaft for slidable engagement with a bore surface of the pump housing. It has been recognized however that a mechanical seal may sometimes produce a squeaking noise in operation because of slipping movements of the seal. Efforts have hithertofore been made for solving the problem. Examples of seals which may substitute for conventional mechanical seals are those having lip seals or seal devices using a magnetic fluid as disclosed for example by the Japanese Laid-Open Utility Model Publication No. Hei 1-99997 (published on Jul. 5, 1989), Japanese Utility Model Publication No. Hei 6-29517 (published on Aug. 10, 1994) and Japanese Patent Publication No. Hei 4-72110 (published on Nov. 17, 1992).
It should however be noted that these sealing structures are not satisfactory since the sealing structures are always subjected to water pressure. The sealing members may show unsatisfactory durability under prolonged contact with water. Further, the sealing members may fail under high water pressure which may be produced in operation. As the results, the sealing structures as proposed by the aforementioned Japanese patent or utility model applications do not show satisfactory reliability.